Many drugs are supplied to pharmacies in a dry or lyophilized form. These drugs are often supplied in rubber stoppered vials with a small portion of their internal volume containing the dry or lyophilized powder. Before such drugs can be used, the lyophilized powder must be dissolved in a sterile liquid. Aftr the lyophilized powder has been dissolved, it can then be extracted from the vial in small unit doses.
In the past, there has been a problem with quickly injecting the sterile dissolving liquid into the mixing vial. Small hypodermic needles with a sharpened beveled forward end, restricted liquid flow to a slow rate. Larger diameter double cut hypodermic needles sometimes cored the rubber stopper causing the needle to plug or a small rubber particle to fall into the vial. In addition, double cut hypodermic needles directed the liquid in a straight longitudinal stream causing its mixing force to be directed to only a small area near the center of the vial.
Also, with conventional metal hypodermic needles, there was a problem with pressure buildup. As liquid began to fill the vial, air within the vial was compressed. Upon removing the liquid filling syringe needle, the compressed air remained in the vial. Subsequently, when withdrawing small samples of the dissolved medicament from the vial, the operator had to be careful the pressure did not urge a plunger of a unit dose syringe rearwardly to inadvertently cause an overdose in the syringe.